I ran into a wild shiny clamperl with its regular texture and eventually figured out the following:

When a shiny clamperl is spawned far away, it doesn't have a shiny texture and will default to its regular one.
When you move away from one that's currently showing shiny texture, it shows the pink/black missing texture further away.

http://i.imgur.com/4E3fPRn.gifv
http://i.imgur.com/Z9pT9VG.png

Gorebyss and Huntail seem fine.